In the present day, various types of processing apparatus are employed to treat or process substrates with ions. For processing substrates such as semiconductor substrates, ions may be used to etch layers or features on a substrate. Ions may also be used to deposit a layer or structures on a substrate, to implant a species into a substrate, or to amorphize a substrate. Techniques have also been developed to monitor processing of a substrate in order to control the processing of a substrate.
In known techniques for etching a substrate, such as reactive ion etching (RIE), etch stop layers may be provided within a substrate to reduce etching rate so etching may be ended at a target region or depth of the substrate. Etching of a layer or layers within a substrate may also be controlled by a timed etch approach. In timed etching, a thickness of a layer and etch rate of the layer may be known or determined a priori, so etching of a substrate is halted at a predetermined time. Such a timed etch method does not account for variation in layer thickness between substrates, or variation in etch rate of a processing apparatus over time.
Accordingly, techniques to monitor a substrate during processing have been developed to measure so-called process endpoint. For example, during etching of a given layer by ions, optical emission spectroscopy has been deployed to monitor changes in chemical species emitted into the gas phase during etching. Thus, a change in intensity of a signal from a given element may indicate when a layer has been removed. Other techniques such as in-situ spectroscopic ellipsometry may be employed to monitor removal of dielectric films, for example. In the aforementioned techniques, disadvantageously, background signals may need to be filtered to properly interpret when an endpoint is reached and the detection apparatus used to monitor such signals may entail extensive engineering for compatibility with a processing apparatus. With respect to these and other considerations the present improvements may have been needed.